The shadow army needed to be designed the way it was designed. Humans were capped at how far they could advance and the monsters he faced were too strong for the people at S rank to even take care of. You remember jeju island right? IT was at that point the reader should have noticed that the hunters of the world at S rank, despite their varying internal ranks, were not capable of completely taking care of the mobs. If you wanted him to have allies that could take care of his back then he needed to go to America but even America proved to be troublesome because of a hunter I forget the name of and even then they could not do anything. There's also the fact that the people that were used as catalyst to bring in the gods or w.e from another world took over their hosts and with the MC he was also someone that was to be a host. He's OP AF but he was not turned into a host. If he was then the world would be over already, nothing big would happen.